{"id":90,"date":"2019-09-22T17:49:24","date_gmt":"2019-09-22T17:49:24","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/accnursingpharmacology\/chapter\/3-2-basic-concepts-of-antimicrobial-therapy\/"},"modified":"2025-01-16T22:29:16","modified_gmt":"2025-01-16T22:29:16","slug":"3-2-basic-concepts-of-antimicrobial-therapy","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/accnursingpharmacology\/chapter\/3-2-basic-concepts-of-antimicrobial-therapy\/","title":{"raw":"3.2 Basic Concepts of Antimicrobial Therapy","rendered":"3.2 Basic Concepts of Antimicrobial Therapy"},"content":{"raw":"

Basic Concepts Related to Antimicrobial Therapy<\/h2>\nBefore we learn about antimicrobial medications used to treat infections, we must first understand the basics of microbiology. Let's begin with a review of bacteria. Bacteria are found in nearly every habitat on earth, including within and on humans. Most bacteria are harmless or considered helpful, but some are pathogens. A [pb_glossary id=\"493\"]pathogen [\/pb_glossary]<\/strong> is defined as an organism causing disease to its host. Pathogens, when overgrown, can cause significant health problems or even death.\n\nSpecific bacteria may be identified when a client has an infection by using a culture and sensitivity test or a gram stain test. An antibiotic is selected by the prescribing provider based on the type of bacteria and the mechanism of action of the medication. Antimicrobials are classified as broad-spectrum or narrow-spectrum, based on the variety of bacteria they effectively treat. Additionally, antibiotics are also selected based on their bacteriostatic or bactericidal actions, as well as their mechanism of action. In addition to antibiotics, antimicrobials also include medications used to treat viruses and fungi. These topics will be discussed in more detail in this section, along with the issue of antibiotic resistance.\n

Culture and Sensitivity<\/h3>\nWhen a client presents with signs or symptoms of an infection, health care providers will begin the detective work needed to identify the source of the infection. A [pb_glossary id=\"494\"]culture[\/pb_glossary]<\/strong> is a test performed to examine different body substances for the presence of bacteria or fungus.[footnote]This work is a derivative of Microbiology<\/a> by OpenStax<\/a> licensed under CC BY 4.0<\/a>. Access for free at https:\/\/openstax.org\/books\/microbiology\/pages\/1-introduction<\/a>[\/footnote]<\/sup> These culture samples are commonly collected from a client's blood, urine, sputum, or wound bed.\n\nNurses are typically responsible for the collection of culture samples and must be conscientious to collect an accurate sample and to obtain the sample prior to the administration of antibiotics. Antibiotic administration prior to obtaining a sample causes inaccurate culture results and can complicate the client's recovery.\n\nAfter culture samples are collected, they are incubated in a solution that promotes bacterial or fungal growth and spread onto a special culture plate.[footnote]Kristof, K., & Pongracz, J. (2016). Interpretation of blood microbiology results - function of the clinical microbiologist. The Journal of the International Federation of Clinical Chemistry and Laboratory Medicine, 27<\/em>(2), 147-155. https:\/\/www.ncbi.nlm.nih.gov\/pmc\/articles\/PMC4975230\/<\/a>[\/footnote]<\/sup> Clinical microbiologists subsequently monitor the culture for signs of organism growth to aid in the diagnosis of the infectious pathogen. For this reason, it typically takes a one to five days for a client's culture results to be reported by the lab.\n\nA [pb_glossary id=\"495\"] sensitivity analysis [\/pb_glossary]<\/strong> is often performed to select an effective antibiotic to treat the microorganism. If the organism shows [pb_glossary id=\"496\"]resistance [\/pb_glossary]<\/strong> to the antibiotics used in the test, the provider knows these antibiotics will not provide effective treatment for the client's infection.\n\nSometimes a client may begin antibiotic treatment for an infection based on common bacterial causes, but after the culture and sensitivity results are reported, the client is switched to a different, more effective antibiotic based on the culture and sensitivity results. The nurse is responsible for monitoring culture and sensitivity results to ensure the prescribed antibiotic therapy is effective and notifying the prescribing provider of any concerns.[footnote]Vorvick, L. (Ed.). (2019, February 7). Sensitivity analysis.<\/em> https:\/\/medlineplus.gov\/ency\/article\/003741.htm<\/a> [\/footnote]<\/sup>\n

Gram-Positive vs. Gram-Negative<\/h3>\nA [pb_glossary id=\"497\"]gram stain [\/pb_glossary]<\/strong> is another type of test that is used to assist in classification of bacteria. Gram stains are useful for quickly identifying if bacteria are \u201c[pb_glossary id=\"729\"]gram-positive[\/pb_glossary]<\/strong>\u201d or \u201c[pb_glossary id=\"728\"]gram-negative[\/pb_glossary]<\/strong>,\u201d based on the staining patterns of their cellular walls. Utilizing gram stain allows microbiologists to look for characteristic staining patterns when they examine organisms under a microscope, with a violet color for gram-positive infections or a red\/pink color for gram-negative infections.[footnote]This work is a derivative of Microbiology<\/a> by OpenStax<\/a> licensed under CC BY 4.0<\/a>. Access for free at https:\/\/openstax.org\/books\/microbiology\/pages\/1-introduction<\/a>[\/footnote]<\/sup> Identification of bacteria as gram-positive or gram-negative assists the health care provider in quickly selecting an appropriate antibiotic to treat the infection, without waiting for culture and sensitivity results.\n

Sample Gram-Positive Infections<\/h4>\nExamples of gram-positive bacteria are Streptococcus<\/em> and Staphylococcus<\/em>. Streptococcus<\/em>, whose name which comes from the Greek word for \"twisted chain,\" is responsible for many types of infectious diseases in humans, especially in the skin or soft tissues.\n\nStreptococcus pyogenes<\/em> is a type of \u03b2-hemolytic Streptococcus.<\/em> This species is considered a \"pyogenic pathogen\" because of the associated pus production observed with infections it causes (see Figure 3.1[footnote]\u201cOSC Microbio 04 04 Strep.jpg<\/a>\u201d by CNX OpenStax is licensed under CC BY 4.0<\/a>. Access for free at https:\/\/openstax.org\/books\/microbiology\/pages\/4-4-gram-positive-bacteria<\/a>[\/footnote]<\/sup> for an image of Streptococcus<\/em> undergoing gram staining). Streptococcus pyogenes<\/em> is the most common cause of bacterial pharyngitis (i.e., strep throat); it is also a common cause of various skin infections that can be relatively mild (e.g., impetigo) or life-threatening (e.g., necrotizing fasciitis, also known as flesh-eating disease).[footnote]This work is a derivative of Microbiology<\/a> by OpenStax<\/a> licensed under CC BY 4.0<\/a>. Access for free at https:\/\/openstax.org\/books\/microbiology\/pages\/1-introduction<\/a>[\/footnote]<\/sup>\n\n[caption id=\"attachment_89\" align=\"aligncenter\" width=\"300\"]\"Photos Figure 3.1 Gram Stain Specimen Streptococcus[\/caption]\n\nStaphylococcus<\/em> is a second example of a gram-positive bacteria. The bacteria Staphylococcus<\/em> comes from a Greek word for \"bunches of grapes,\" which describes their microscopic appearance in culture. Strains of Staphylococcus aureus<\/em> cause a wide variety of infections in humans, including skin infections that produce boils, carbuncles, cellulitis, or impetigo.\u00a0See Figure 3.2[footnote]This work is a derivative of \u201cCDC-10046-MRSA.jpg<\/a>\u201d by Janice Haney Carr, Centers for Disease Control and Prevention and is licensed under CC0<\/a>[\/footnote]<\/sup> for an image of Staphylococcus<\/em> bacteria microscopically.\n\n[caption id=\"attachment_89\" align=\"aligncenter\" width=\"300\"]\"Photo Figure 3.2 Staphylococcus Aureus[\/caption]\n\nMany strains of Staphylococcus aureus<\/em> have developed resistance to many antibiotics. Examples of antibiotic-resistant strains are [pb_glossary id=\"499\"] methicillin-resistant Staphylococcus aureus (MRSA) [\/pb_glossary]<\/strong> and [pb_glossary id=\"500\"]vancomycin-resistant Staphylococcus aureus (VRSA) [\/pb_glossary]<\/strong>. Antibiotic resistant strains are difficult to treat because they exhibit resistance to nearly all available antibiotics. Because they are difficult to treat with antibiotics, infections can be lethal. MRSA and VRSA are also very contagious, posing a serious threat in hospitals, nursing homes, dialysis facilities, and other places where there are large populations of elderly, bedridden, and\/or immunocompromised clients.[footnote]This work is a derivative of Microbiology<\/a> by OpenStax<\/a> licensed under CC BY 4.0<\/a>. Access for free at https:\/\/openstax.org\/books\/microbiology\/pages\/1-introduction<\/a>[\/footnote]<\/sup>\n

Sample Gram-Negative Infections<\/h4>\nGram-negative bacteria have a great ability to cause disease in humans and can infect almost all body systems, such as the digestive system, nervous system, urinary system, and bloodstream. A common gram-negative bacterium is Escherichia coli<\/em> (E. coli). E. coli is a common cause of urinary tract infections due to its normal presence in the gastrointestinal tract that can contaminate the urinary tract and cause infection.\n\nOther gram-negative bacteria can cause severe, sometimes life-threatening, disease. The genus Neisseria<\/em>, for example, includes the bacteria Neisseria gonorrhoeae <\/em>and\u00a0causes the sexually transmitted infection gonorrhea, and Neisseria meningitidis <\/em>causes\u00a0bacterial meningitis. See Figure 3.3[footnote]\u201cOSC Microbio 04 02 Neisseria.jpg<\/a>\u201d by CNX OpenStax<\/a> is licensed under CC BY 4.0<\/a>. Access for free at https:\/\/openstax.org\/books\/microbiology\/pages\/4-2-proteobacteria<\/a>[\/footnote]<\/sup> for an image of Neisseria meningitides<\/em>.\n\n[caption id=\"attachment_89\" align=\"aligncenter\" width=\"300\"]\"Photo Figure 3.3 Neisseria Meningitidis[\/caption]\n

Broad-Spectrum vs. Narrow-Spectrum Antimicrobials<\/h3>\nThe spectrum of activity of an antibiotic is considered by providers when selecting an antibiotic to treat a client's infection. A [pb_glossary id=\"501\"]narrow-spectrum antimicrobial [\/pb_glossary]<\/strong> targets only specific subsets of bacterial pathogens.[footnote]This work is a derivative of Microbiology<\/a> by OpenStax<\/a> licensed under CC BY 4.0<\/a>. Access for free at https:\/\/openstax.org\/books\/microbiology\/pages\/1-introduction<\/a>[\/footnote]<\/sup> For example, some narrow-spectrum drugs target gram-positive bacteria whereas others target gram-negative bacteria.\n\nA [pb_glossary id=\"502\"]broad-spectrum antimicrobial [\/pb_glossary]<\/strong> targets a wide variety of bacterial pathogens, including both gram-positive and gram-negative species. There are many reasons why a broad-spectrum antibiotic is prescribed. Broad-spectrum antibiotics may be prescribed while culture results are pending and then a narrow-spectrum antibiotic may be prescribed based on the culture and sensitivity results. Broad-spectrum antimicrobials are also used for polymicrobial infections (mixed infections with multiple bacterial species) or to prevent infections that may occur from surgery or invasive procedures. Additionally, broad-spectrum antimicrobials may be selected to treat an infection that has not responded to a narrow-spectrum antibiotic because of presumed antibiotic resistance.[footnote]This work is a derivative of Microbiology<\/a> by OpenStax<\/a> licensed under CC BY 4.0<\/a>. Access for free at https:\/\/openstax.org\/books\/microbiology\/pages\/1-introduction<\/a>[\/footnote]<\/sup>\n

Effects on Microbiome and Potential Superinfection<\/h4>\nA risk of using broad-spectrum antibiotics is they affect an individual's microbiome. An individual's microbiome consists of microbes that are both helpful and potentially harmful. Most are symbiotic (where both the human body and microbiota benefit), but some are pathogenic and cause disease. Broad-spectrum antibiotics can cause a disturbance in the balance between symbiotic and harmful microbiota, resulting in disease.[footnote]Harvard T.H. Chan School of Public Health. (n.d.). The Microbiome. https:\/\/www.hsph.harvard.edu\/nutritionsource\/microbiome\/<\/a>[\/footnote]<\/sup>\n\nFor example, in the vagina, normal flora compete with opportunistic pathogens like Candida albicans<\/em>. This competition prevents yeast infection by limiting the availability of nutrients and inhibiting the growth of Candida<\/em>, keeping its population in check. However, when this balance is disrupted by an antibiotic, a yeast infection can occur.\n\nSimilar competitions occur between normal flora and potential pathogens in the gastrointestinal tract. Treatment with antibiotics can significantly deplete the normal flora of the gastrointestinal tract, providing an opportunity for pathogenic bacteria such as [pb_glossary id=\"631\"]Clostridium difficile (C-diff)[\/pb_glossary]<\/strong> to cause diarrheal infection. Diarrhea caused by C-diff can be severe and potentially lethal. Interestingly, a recent strategy for treating recurrent C-diff infections focuses on restoring normal flora by transplanting fecal matter from a healthy donor with normal flora. See Figure 3.4[footnote]This work is a derivative of \u201cClostridium difficile 01.jpg<\/a>\u201d by Lois D. Wiggs at Centers of Disease Control and Prevention and is licensed under CC0<\/a>[\/footnote]<\/sup> for an image of C-diff microscopically.\n\n[caption id=\"attachment_89\" align=\"aligncenter\" width=\"300\"]\"Photo Figure 3.4 Clostridium Difficile[\/caption]\n\nAn infection caused by a disruption of the individual's microbiome is also referred to as a [pb_glossary id=\"503\"]superinfection [\/pb_glossary]<\/strong> (i.e., a secondary infection in a client having a preexisting infection). A superinfection develops when the antibiotic intended for the existing infection also kills the protective microbiome. An example of a severe superinfection is pseudomembranous colitis caused by C-diff, which can be fatal.[footnote]This work is a derivative of Microbiology<\/a> by OpenStax<\/a> licensed under CC BY 4.0<\/a>. Access for free at https:\/\/openstax.org\/books\/microbiology\/pages\/1-introduction<\/a>[\/footnote]<\/sup>\n\nProbiotics, such as lactobacillus, are commonly recommended for individuals taking antibiotics to restore normal flora into the gastrointestinal system and prevent diarrhea, yeast infections, and other superinfections.\n

Recap<\/h4>\n